Color Theory COMP575 Micah Taylor Overview Welcome comp770! Today: Color representation Video hardware Gamma Color theory Homework Color representation How to store colors in the computer? Color representation Grays How many colors are there? How many bits are needed? What does the stored value represent? What if there are many more colors between these (not shown)?
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Color TheoryCOMP575
Micah Taylor
OverviewWelcome comp770!
Today:Color representationVideo hardwareGammaColor theoryHomework
Color representationHow to store colors in the computer?
Color representationGrays
How many colors are there?How many bits are needed?What does the stored value represent?What if there are many more colors between these (not shown)?
Color representationGrays
Number of bits: 8, 32(int), 32(float)Colors represented: 256, 2^32 (4.3 billion)Meaning: radiant intensity, reflected intensity, arbitrary
Color representationBlues
How many bits are needed to mix blue in?What should we call the values we are storing?Should all values use the same number of bits?
Color representationBlues
Number of bits: 8, 32(int), 32(float) (per channel)Channel names: brightness, lightness, blueness, blue, gray...Colors represented: 256, 2^32 (4.3 billion) (per channel)Meaning: radiant intensity, reflected intensity, ratio of blue, arbitrary
Color representationValue representation
Bit countInteger, float
Color modelRed, green, blueCyan, magenta, yellow, black
Digger (1983) Crazy Cars (1987)
Hue, saturation, valuemore...
Format detailsPaletteChannel layoutmore...
Color representation
Battlezone (1980)1 bit, colored with red and green filters.
Color representation
CGA 4 color mode.
Color representation
Jazz Jackrabbit (1994) Descent (1994)
CD-Man (1992)EGA 16 color mode.
Color representation
VGA 256 color mode.
Color representation
Diablo (1997)256 colors.
Color representation
Palettes for 16 colors, 256 colors, 4096 colors, and 65536 colors.
Color representation
24 bit
Color representation
16 bit
Color representation
12 bit
Color representation
8 bit
Color representation
4 bit
Color representation
Color representation
2 bit
Color representation
1 bit
OverviewColor representationVideo hardwareGammaColor theoryHomework
Video hardwareCathode Ray Tube (CRT)Liquid Crystal Display (LCD)
Fig 2.4, H&B
Others...
Other output include hard copies, like printouts.
Video hardwareCathode Ray Tube (CRT)
Video hardwareCathode Ray Tube (CRT)
Video hardwareLiquid Crystal Display (LCD)
Fig 2.4, H&B
Bottom: input, left side: output
OverviewColor representationVideo hardwareGammaColor theoryHomework
Gamma correctionResponse curve
Gamma correctionResponse curve
Gamma correctionResponse curve
Gamma correctionWhat functions do these curves look like?
They are similar to sqrt(x) and x^2.
Gamma correctionHumans perception is not always linear
Sound volumeWeightBrightness
Weber's law
Human perception changes with intensity.
Gamma correction
Camera
Sean McHugh - Cambridge in Colour
Eyes
Camera
Eyes
Devices and programs use linear dataHumans perceive logarithm data
Gamma correctionFull gray gradiant:
Linear gradiant:
Gamma correctionFull gray gradiant:
Gamma gradiant:
Sean McHugh - Cambridge in Colour
Gamma correction
Gamma correctionOutput devices have their own gamma curve!Normalizes image gamma back to linear luminance
Sean McHugh - Cambridge in Colour
Gamma correctionGamma encoding
Applied when creating image
Gamma decodingApplied at output
OverviewColor representationVideo hardwareGammaColor theoryHomework
Color TheoryMixing modes
LightColor spaces
Color TheoryMixing modes
SubtractiveMixes reflective materialsRemoves light (absorption)
Color TheoryMixing modes
AdditiveMixes emmissive materialsAdds light
Color TheoryLight
We only care about tiny visible portion
ROYGBV380
450
495
570
590
620
750
Color TheoryHuman eyes have 2 types of sensors
Rods - very sensitive, no colorCones - color
400 450 500 550 600 650 700Wavelength (nm)
Nor
mal
ized
con
e re
spon
se (l
inea
r ene
rgy)
S M L
Color TheoryCIE 1931 standard
Color TheoryCIE 1931 gamut
Color TheoryModern sRGB gamut
OverviewColor representationVideo hardwareGammaColor theoryHomework
HomeworkQuestions?
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